1. Field of the Invention
The present invention relates to a liquid lens for use in a projection television.
2. Description of Background Information
As shown in FIG. 2, a lens for use in a projection television typically comprises: a liquid lens 3 made of a coolant which covers a fluorescent surface 1a of a CRT 1; a first group of lenses g.sub.1 arranged on the left side in the diagram of the liquid lens 3; and a second group of lenses g.sub.2 arranged adjacent to the first group of lenses g.sub.1. The liquid lens 3 is enclosed in a coupler 2 attached to the fluorescent surface 1a of the CRT 1. A meniscus lens 2a is formed at the front surface of the coupler 2. The first group of lenses g.sub.1 and the second group of lenses g.sub.2 form a power lens group G, and the first and second groups of lenses g.sub.1 and g.sub.2 together with the meniscus lens 2a forms a projection lens L.
In using such a lens L, in order to meet the requirement of various sizes of the screen, a distance between the power lens group G end the meniscus lens 2a is changed, thereby changing the projection magnification. When the projection magnification is changed as mentioned above, however, the image positions deviate in the central portion and peripheral portion of the screen, through the so-called image plane curving phenomenon. As a correcting method for preventing such a phenomenon, the distance between the first group of lenses g.sub.1 and the second group of lenses g.sub.2, for instance, in the power lens group G is changed or one or a plurality of lenses in the power lens group G are exchanged with other lenses (not shown) in accordance with the screen size. Alternatively, the focal length or the aspherical characteristic of the meniscus lens 2a is changed for such correction purposes.
As prior art relating to the present invention, U.S. Pat. No. 4,725,755 to Hasegawa describes a liquid lens made of a mixed liquid of ethylene glycol and glycerine. In U.S. Pat. No. 4,780,640 to Hasegawa a liquid lens is made of a mixed liquid of 1.3-butylene glycol and glycerine. U.S. Pat. No. 4,838,665 to Yoshioka et al. describes a liquid lens made of a liquid and a gel.